Problem with On-The-Fly PlayReady Encryption

Using Wowza Media Server 3, I tried both the key file way and server-api way, but I always got an error message on wowza server saying "PlayReadyEncryptor.encryptChunkCTR: java.lang.NullPointerException", and stuck in a "media error 3192" message when trying to play with Silverlight player.

I logged some messages at license server(PlayReady) and it showed that the license issuing functions correctly.